To analyze the basic Electrical circuits and to understand the working of Electrical machines and its application in various fields.

1. 18BEPS02- Electrical
Technology
G. Mahalakshmi Malini, AP/ECE
Avinashilingam Institute for Home Science and Higher Education for
Women, School of Engineering
Department of Electronics and Communication Engineering
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2. Objective:
• To analyze the basic Electrical circuits and to understand
the working of Electrical machines and its application in
various fields.
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3. Refernces:
• Sudhakar, A., Shyam Mohan S. Palli, “Circuits and Networks”, Tata
McGraw Hill Publishing Company Limited, Fifth Edition, ISBN
9789339219604, 2015.
• Cotton.H, “Electrical Technology”, 7th edition, New Delhi, CBS
Publishers, Reprint 2005.
• PILLAI, S.K.”A First Course On Electrical Drives” 3rdEdition.LWiley
Eastern Ltd, New Delhi.2012.
• Joseph Edminister and Mahmood Nahri, “Electric Circuits”, fifth
Edition, Tata McGraw Hill New Delhi, 2008.
• V.K.Mehta,Rohit Mehta,”Pinciples of Electrical Machines”, S.Chand &
company Ltd. Reprint 2006.
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4. Unit – I Basics of Circuit Analysis
What is Circuit Analysis?
• In an electrical circuit the process of studying and analyzing the various
electrical quantities involved, especially the nodal voltages and currents
through calculations, is known as circuit analysis.
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5. • To be able to solve the various problems generally involved in practical
electrical circuits, it would be first important to learn the following basic
units of electricity:
• Current (I): The unit of current is Ampere (A) and is defined as the
quantity of current forced by a pressure of one volt through a resistance of
one Ohm.
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6. • Voltage (V): The unit of voltage is Volt (V) and is defined as amount of pressure
required to force a current of one ampere through a resistance of one Ohm.
• While talking of voltages we should be careful about the following two terms:
• Electromotive Force (E): It is the voltage that exists across the terminals of a
battery or dynamo which is not connected to any external circuit.
• Potential Difference (U): It is the voltage that exists across the terminals of a
battery or dynamo that is connected to an external circuit. It may be calculated using
the below given formula:
• U = (E – Internal resistance of battery or dynamo) × I
• Resistance (Ω): The unit of resistance is Ohm (Ω) and is defined as the amount of
resistance offered by a circuit so that a current of one ampere is allowed to flow
through it at a pressure of one volt.
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7. Questions?
1) What is Ohm's law?
2) What is Ohm's law used for?
3) Why is the Ohm's law important?
4) What are the 3 forms of Ohms law?
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8. Ohm’s Law
What is Ohm's law?
Ohm's law is a law that states that the voltage
across a resistor is directly proportional to the
current flowing through the resistance. Ohm's
law is named for German physicist
Georg Ohm (1789-1854).
A simple formula, Ohm's law, is used to show
the relationship of current, voltage, and
resistance.
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9. Ohms Law describes the relationship between three basic elements of a circuit, The Voltage
(V), Current (I) and Resistance (R) and shows how each of these values are interconnected.
• The most common analogy used to describe this principle is to visualize a series of pipes
with water flowing through them. Each of these values can be associated with a
characteristic of the pipe system.
• Voltage – The force with which water is being pumped into your system, with electronics
we can modify this by using higher voltage (or more) batteries or a higher voltage power
supply.
• Resistance – The Factors which restrict water flow through the pipe, for instance the width
of the pipe or a partial cutoff valve. Resistance in a circuit can be added using resistors of
various types
• Current – The speed at which water which flows through the pipe
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10. Electric Circuits and Network Theorems
• 1. Circuit. A circuit is a closed conducting path through which an electric current either
flows or is intended flow.
• 2. Parameters. The various elements of an electric circuit are called its parameters like
resistance, inductance and capacitance. These parameters may be lumped or distributed.
• 3. Liner Circuit. A linear circuit is one whose parameters are constant i.e. they do not change
with voltage or current.
• 4. Non-linear Circuit. It is that circuit whose parameters change with voltage or current.
• 5. Bilateral Circuit. A bilateral circuit is one whose properties or characteristics are the same
in either direction. The usual transmission line is bilateral, because it can be made to
perform its function equally well in either direction
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11. • 6. Unilateral Circuit. It is that circuit whose properties or characteristics change with
the direction of its operation. A diode rectifier is a unilateral circuit, because it
cannot perform rectification in both directions.
• 7. Electric Network. A combination of various electric elements, connected in any
manner whatsoever, is called an electric network.
• 8. Passive Network is one which contains no source of e.m.f. in it.
• 9. Active Network is one which contains one or more than one source of e.m.f.
• 10. Node is a junction in a circuit where two or more circuit elements are connected
together.
• 11. Branch is that part of a network which lies between two junctions.
• 12. Loop. It is a close path in a circuit in which no element or node is encountered
more than once.
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12. 13. Mesh. It is a loop that contains no other loop within it. For example, the
circuit of Fig. 2.1 (a) has even branches, six nodes, three loops and two meshes
whereas the circuit of Fig. 2.1 (b) has four branches, two nodes, six loops and
three meshes
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13. There are two general approaches to network
analysis
• (i) Direct Method
• Here, the network is left in its original form while determining its different voltages
and currents. Such methods are usually restricted to fairly simple circuits and include
Kirchhoff’s laws, Loop analysis, Nodal analysis, superposition theorem,
Compensation theorem and Reciprocity theorem etc.
• (ii) Network Reduction Method
• Here, the original network is converted into a much simpler equivalent circuit for
rapid calculation of different quantities. This method can be applied to simple as
well as complicated networks. Examples of this method are : Delta/Star and
Star/Delta conversions. Thevenin’s theorem and Norton’s Theorem etc.
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14. Questions?
1) What is kirchoff’s law?
2) What is Kirchhoff's first law?
3) What is Kirchhoff's Second law?
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15. Kirchoff’s Law
• two laws concerning electric networks in which steady currents are flowing.
1. Kirchhoff’s Point Law or Current Law (KCL) It states as follows : in any electrical
network, the algebraic sum of the currents meeting at a point (or junction) is zero.
Put in another way, it simply means that the total current leaving a junction is equal
to the total current entering that junction.
I1 + (−I2) + (−I3) + (+ I4) + (−I5) = 0 or
I1 + I4 −I2 −I3 −I5 = 0 or I1 + I4 = I2 + I3
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16. 2. Kirchhoff’s Mesh Law or Voltage Law (KVL) It states as follows :
The algebraic sum of the products of currents and resistances in each of the
conductors in any closed path (or mesh) in a network plus the algebraic sum of
the e.m.fs. in that path is zero. In other words, Σ IR + Σ e.m.f. = 0 ...round a
mesh It should be noted that algebraic sum is the sum which takes into account
the polarities of the voltage drops.
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17. Determination of Voltage Sign
(a) Sign of Battery E.M.F – Fig 2.3
(b) (b) Sign of IR Drop – Fig 2.4
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